Yii2: Standalone validation not triggering client validation - validation

Question

Validation functions don't work.
Validation customs rules are not applied to the usernmane field
module dektrium/user
PHP 7.1
Yii 2.0.16
Already try all from here: https://www.yiiframework.com/doc/guide/2.0/en/input-validation (Inline Validators and Standalone Validators)
Model Agent :
class Agent extends Profile
{
public $username;
public $password;
public $password2;
public function rules()
{
$rules = [
['username', AgentValidator::className()],// it's not work
[['email'], 'email'], // it's work
['password2', 'compare', 'compareAttribute' => 'password', 'message' => 'Пароли должны совпадать'],//// it's work
];
return array_merge(parent::rules(), $rules);
}
}
AgentValidator.php
<?php
namespace app\components;
use yii\validators\Validator;
class AgentValidator extends Validator
{
public function validateAttribute($model, $attribute)
{
if (User::findOne(['username' => $this->$attribute]]) {
$this->addError($attribute, 'Такой логин уже занят');
}
}
}

Answer 1

You are using standalone validator and you want the frontend validation to be working along with the backend so you need to override the yii\validators\Validator::clientValidateAttribute() in your Standalone validator AgentValidator, which returns a piece of JavaScript code that performs the validation on the client-side.
Within the JavaScript code, you may use the following predefined variables:
attribute: the name of the attribute being validated.
value: the value being validated.
messages: an array used to hold the validation error messages for the attribute.
deferred: an array which deferred objects can be pushed into.
You can go through the section Implementing Client Validation to read in detail.
Apart from everything listed above you have a mistake in your validator code User::findOne(['username' => $this->$attribute]], you need to use $model->$attribute rather than $this->$attribute which will never get the exact value entered in the form. You might have mistakenly added it from the model.
Your current validator should be like below
<?php
namespace app\components;
use yii\validators\Validator;
class AgentValidator extends Validator
{
public $message='Такой логин уже занят';
public function validateAttribute($model, $attribute)
{
if (User::findOne(['username' => $model->$attribute])!==null)
{
$model->addError($attribute, $this->message);
}
}
public function clientValidateAttribute($model, $attribute, $view) {
//check if user exists
$userExists = User::findOne(['username' => $model->$attribute])!==null;
$message = json_encode($this->message, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
return <<<JS
if($userExists){
messages.push($message);
return;
}
JS;
}
}

Answer 2

So, Thank Muhammad Omer Aslam for right answer.
Yii2 does't generate any js code for validation by custom rules. Therefore it is necessary to add a check to the controller and the form
For me it:
Controller
if (\Yii::$app->request->isAjax) {
\Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;
$model->load(\Yii::$app->request->post());
return \yii\widgets\ActiveForm::validate($model);
}
Form
$form = ActiveForm::begin([ 'enableAjaxValidation' => true]);